1. Field of the Invention
This invention relates to a metal-made carrier body, for carrying thereon an exhaust gas cleaning catalyst, which is generally provided as an exhaust gas cleaning means at a midpoint of an exhaust system of an automobile.
More particularly, the invention relates to a metal-made carrier body for carrying thereon an exhaust gas cleaning catalyst, in which the individual components of the carrier body can perform their complete function without separation, breakage or other damage when used even in severe environments.
2. Description of the Related Art
Conventional metal-made carrier bodies of the above sort, which are adapted to carry an exhaust gas cleaning catalyst thereon, include those having a structure formed by laminating at least one sheet-like metal band and at least one corrugated metal band in layers or rolling them together into a multi-layered composite body so as to increase the carrying area per unit volume, namely, so as to increase as much as possible the effective area of contact between exhaust gas and the exhaust gas cleaning catalyst per unit volume and to further reduce the own weight of the metal-made carrier body to a maximum possible extent.
For example, a sheet-like band made from a heat-resistant then sheet of Fe-Cr (iron-chromium) steel having a thickness of 0.1 mm or less and a corrugated band made from another thin metal sheet of the same kind are superposed one over the other to have areas of contact therebetween. They are then rolled together spirally into a multi-layered composite body defining many network-patterned gas flow passages along a central axis thereof for allowing exhaust gas to pass therethrough. The multi-layered composite body is enclosed within a tubular metal casing which has a single-layer structure and opens in opposite ends thereof. The members of the multi-layered composite body, i.e., the sheet-like band and corrugated band are put together into a vibration-proof structure.
Namely, the sheet-like band and corrugated band as well as the metal casing are put together at the areas of contact therebetween by welding as disclosed in Japanese Patent laid-Open Publications Nos. 13462/1979 and 1585/1982, for example, or by brazing as disclosed in Japanese Patent Laid-Open Publications Nos. 4373/1981 and 199574/1986, for example.
However, the metal-made carrier body produced by the above conventional joining means cause the following structural problems.
The metal-made carrier body of this type is used in severe thermal environments and hence requires adequate durability against any breakage, cracking or separation of the members making up the carrier body. In the exhaust system of an automobile, the members of the carrier body are subjected to strains (hereinafter called "thermal strains") due to the large difference between their coefficients of thermal expansion (volume expansion and linear expansion) under the severe cooling and heating cycle of from .+-.20.degree. C. to 900.degree. C. When their separation begins, these members would be cracked or otherwise broken as vibrations from an internal engine or an automobile body are added. With the conventional construction, such separation and cracking can be prevented only incompletely.